Photosensitizers and photoinitiators, used for the photoinduced free radical polymerization of monomers, are important in radiation curable coatings, bulk polymerization, and the graphic arts. Polymeric photosensitizers are also known in the art. Advantages of polymeric photosensitizers and photoinitiators over low molecular weight materials are: greater processability, lower likelihood of loss of photosensitizer from photosensitive coatings through sublimation or leaching, and generally lower toxicity. Any improved efficiency in the utilization of incident light to photoinitiate polymerization allows for shorter exposure times or lower light intensities in the photocuring process, whether on a web, in solution or in graphic arts applications.
Use of polymeric photoinitiators to allow polymerization was described by Flamigni et al. [Eur. Polym. J., 20, 171 (1984)], and other examples can be found in U.S. Pat. Nos. 3,429,852 and 3,622,848.
Carbonyl containing polymeric quaternary ammonium salts as photoinitiators of polymerization have been reported by Shibanov and Protsyuk [Russian Pat. No. USSR 787,416, see Chemical Abstracts, 94, 122299r, 1981)]. Photoinitiated polymerization of methyl methacrylate with poly(methylisopropenyl ketone) was taught by Naito et al. [Kobunshi Ronbunshu 36, 777 (1979)]. Carlini et al. [Polymer, 24, 599 (1983)] cured acrylic compositions with benzophenone/dimethylaniline-substituted polymers.
Use of certain photosensitizers with onium salts for free radical generation and initiation of polymerization is also well known in the art. The technique of photogeneration of free radicals using onium salts for free radical photopolymerization and cationic photopolymerization has found applications in printing, duplication, copying, and other imaging systems--see J. Kosar in Light Sensitive Systems: Chemistry and Application of Nonsilver Halide Photographic Processes, Wiley, New York, 1965, pp 158-193. Onium salt photosensitization by polymeric photosensitizers has not previously been reported. Photosensitization of iodonium salts for free radical and cationic polymerization using low molecular weight (non-polymeric) photosensitizers has been taught in U.S. Pat. Nos. 3,729,313, 3,741,769, and 3,808,006; and in U.S. Pat. Nos. 4,026,705, 4,069,054, 4,250,053, 4,394,403 and British Pat. No. 2,070,614 respectively.
Monomeric Mannich bases used as free radical photoinitiators has been described in laid open Japanese patent application JA54-37182.
Whereas polymeric Mannich bases derived from ketones are known, (see for example Tsuchida et al. J. Polymer Sci., Letters Ed., 14, 103 (1976) and Angeloni et al. Polymer Commun., 24, 87 (1983) and references cited therein), their use as photosensitizers as taught in this invention is novel.
Thus, what the background art has not taught but what this invention teaches is the synthesis of new Mannich polymers and their general use as photosensitizers for iodonium salts for use in the initiation of free radical polymerization of vinyl monomers. Moreover, these Mannich polymers are unexpectedly more efficient as photosensitizers than are the non-polymeric photosensitizers.